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Using the parameters used previously, and $C_{eff}$ = 0.5, $\eta$ = 0.6, and $Trec$ = 100 K, we can make the following comparison of the variations of $Tcal$
Item $T_{cab}$ $Trec$ $F_{eff}$ $C_{eff}$ $\eta$
Typical Error 2 K 10 K 0.01 0.02 0.02
Induced variation (in %) 0.7 0.3 1.3 2.0 -0.5

This shows that the maximum effect is from $C_{eff}$ if this method is used, from $F_{eff}$ otherwise. It also indicates that the ``reduced chopper'' calibration is not a good technique, but a switchable attenuator should be used instead.

Gildas manager 2018-03-19